The present invention relates to a process for highly accurate pattern formation by using an active beam sensitive resin.
Pattern formation by using an active beam sensitive resin is carried out by coating various substrates with the resin to form a resin film, subjecting the film to pattern exposure with an active beam such as light, electron beam or X-ray, and then developing with a developing solution for dissolving the film only at unnecessary parts thereof.
Prior processes for forming patterns are conducted by exposing the active beam sensitive resin to cause reaction of the resin or sensitive groups therein, resulting in a change of solubility of the resin to the developing solution. The simplest mechanism of such solubility change is based on an increase in molecular weight or on formation of a network structure by intermolecular crosslinking reaction of the resin. However, a process in which only the crosslinking reaction is employed is not suitably applied to accurate patterning, since a sufficient solubility change cannot be obtained solely by the crosslinking reaction, and thus the crosslinked resin parts may swell with a developing solution. Therefore, for the purpose of highly accurate patterning, a mechanism is employed whereby polarity of the resin is varied by the reaction of sensitive groups to change the solubility of the resin to the developing solution. Change polarity of the resin itself varies its affinity for the developing solution and can decrease the swelling of the resin during the development. Thus highly accurate patterning is possible, and formation of a positive pattern can be achieved, which could not be realized by the crosslinking reaction. At present, studies are actively proceeding on high quality pattern formation using the above mechanism. These studies are classified into two area; one is to enhance characteristics of materials of the resin itself, and another is to improve processes for forming patterns. As to the latter area there are some proposals under study to modify a coated film of an active beam sensitive resin.
Regarding an active beam sensitive resin, many sensitive groups can cause change in its polarity. However, sensitive groups which can bring about polarity change which causes a solubility change that is large enough with respect to the developing solution are very limited. Since this solubility change to the developing solution determines the form of patterns finally formed, in the prior pattern formation process insufficient solubility change made it very difficult to form good patterns correctly corresponding to a pattern mask. Even if a large enough change in solubility is attained, there are extreme restrictions in practical use; difficult process control because of very strict developing conditions, and a higher cost of the resin due to the large amount of sensitive groups required.
On the contrary, with respect to improvement in pattern forming processes, there is an effective method to enhance quality the pattern in which a decrease in film thickness of the pattern during development is restrained, which thereby improves contrast of the obtained pattern and its dimensional accuracy. As examples of this process, the following methods have been propsosed a resist for semi-conductors, in which an alkalizing treatment is adopted on the resist film before exposing (Semicon News 1988 Sept., p. 90-101), and a method in which a metal complex layer is formed on an organic resist film before exposing (JP-A-143254/1990). However, those methods are not suitable for practical use, because they need additional processes and strict conditions for obtaining the desired effect.
The present inventors have found as a result of various studies that by incorporating a certain ion in an aqueous solution, solubility of a resin can be lowered. As a concrete behavioral change of the dissolution inhibition effect of lowering the solubility of the pattern, the resin becomes difficult to dissolve in a developing solution. Furthermore if an ion content is increased, the resin itself can be modified and becomes difficult to dissolve even in an aqueous solution having a small mount of ions in subsequent steps. Though the cause of that effect is not clear, it supposedly is affected largely by the change in activity of the aqueous solution containing ions. Also the effect will relate to formation of chelate compounds. The degree of the effect remarkably depends on the kind and concentration of ions, and further, is largely affected by characteristics of the resin itself. Thus, it has been found that when using this effect for forming patterns of polarity changeable type active beam sensitive resins, solubility of the resin of the pattern parts can be reduced to inhibit the decrease in film thickness at patterns during developing and the quality of the obtained pattern can be enhanced.
The present invention is intended to solve the aforementioned problems, and its object is to provide a patterning process by which the reaction of the resin by an active beam radiation correctly corresponds to the formed pattern, and by which the process steps are not complicated and are easily controlled.